title: Spatial encoding using the nonlinear field perturbations from magnetic materials.
abstract: OBJECTIVE
  A proof-of-concept study was performed to assess the technical feasibility of using magnetic materials to generate spatial encoding fields.
  
  
  METHODS
  Spatially varying magnetic fields were generated by the placement of markers with different volume susceptibilities within the imaging volume. No linear gradients were used for spatial encoding during the signal acquisition. A signal-encoding model is described for reconstructing the images encoded with these field perturbations. Simulation and proof-of-concept experimental results are presented. Experiments were performed using field perturbations from a cylindrical marker as an example of the new encoding fields. Based on this experimental setup, annular rings were reconstructed from signals encoded with the new fields.
  
  
  RESULTS
  Simulation results were presented for different acquisition parameters. Proof-of-concept was supported by the correspondence of regions in an image reconstructed from experimental data compared to those in a conventional gradient-echo image. Experimental results showed that inclusions of dimensions 1.5 mm in size could be resolved with the experimental setup.
  
  
  CONCLUSIONS
  This study shows the technical feasibility of using magnetic markers to produce encoding fields. Magnetic materials will allow generating spatial encoding fields, which can be tailored to an imaging application with less complexity and at lower cost compared to the use of gradient inserts.
authors.affiliation: Department of Medical Biophysics, University of Toronto, Toronto, Canada; Sunnybrook Research Institute, Physical Sciences Department, Toronto, Ontario, Canada.
authors.forename: Hirad
authors.initials: H
authors.lastname: Karimi
authors.forename: William
authors.initials: W
authors.lastname: Dominguez-Viqueira
authors.forename: Charles H
authors.initials: CH
authors.lastname: Cunningham
mesh_terms: D000465:Algorithms; D001672:Biocompatible Materials / Q000737:chemistry*; D004867:Equipment Design; D019544:Equipment Failure Analysis; D005240:Feasibility Studies; D057918:Fiducial Markers; D006801:Humans; D007089:Image Enhancement / Q000295:instrumentation* / Q000379:methods*; D060526:Magnetic Fields; D008279:Magnetic Resonance Imaging / Q000295:instrumentation* / Q000379:methods*; D059346:Magnets; D008422:Materials Testing; D017711:Nonlinear Dynamics; D019047:Phantoms, Imaging; D015203:Reproducibility of Results; D012542:Scattering, Radiation; D012680:Sensitivity and Specificity
chemical_list: D001672:Biocompatible Materials
keywords: field perturbations; nonlinear spatial encoding; reconstruction; susceptibility